1. Field of the Invention
The present invention relates to an image processor, a vehicle and an image processing method for converting a camera image captured by a camera provided on the vehicle into a projection image for display.
2. Description of the Related Art
Conventionally, driving assistance systems have been proposed in order to allow a driver of a vehicle such as an automobile to check a situation around the vehicle. In such a driving assistance system, a camera captures a region around a vehicle and captured image is displayed on an in-vehicle display.
FIG. 1 shows an example of a driving assistance system including cameras 10_1 and 10_2 provided on a vehicle. In the driving assistance system, the camera 10_1 takes an image of a target region L to capture a left camera image PL, and the camera 10_2 takes images of a target region R to capture a right camera image PR. The driving assistance system is configured to cause an in-vehicle display to display the captured camera images PL and PR.
In such a driving assistance system, a panoramic composition is used as a technique for compositing images captured by a plurality of cameras to generate an image in the wide field of view. The above-described panoramic composition is a technique for generating a composite image by first projecting a plurality of camera images onto a common flat surface or a common cylindrical surface, and then compositing the projected images. Meanwhile, in recent years, a panoramic composition using a cylindrical surface and a spherical surface in combination has been proposed (e.g., Japanese Patent Publication No. 2002-83285).
Note that, in the case of the above-described panoramic composition in which a plurality of captured images are combined while being projected and onto a flat surface, the resultant composite image is partially enlarged in a manner that the closer to the left and right end, the more greatly the image is enlarged, as shown in FIG. 2A. Thus, such a composite image has a problem that the driver has a difficulty in checking the safety around the vehicle in a wide field of view, by using the composite image.
Instead, in the case where a plurality captured images are combined while being projected onto a cylindrical surface, the composite image has advantages that the image can be projected in a wide field of view without having the left and right ends enlarged, as shown in FIG. 2B. However, such a composite image is distorted as a whole, so that an object M located around the vehicle is displayed as a distorted object. Consequently, such a composite image has a problem that the driver has a difficulty in figuring out how far an object is from the vehicle by using the composite image, particularly for an object existing in the traveling direction of the vehicle.
In the panoramic composition disclosed in Japanese Patent Publication No. 2002-83285, in projecting captured images, an image far from a vehicle is projected on a cylindrical surface and an image near the vehicle is projected on a spherical surface, whereby a composite image is generated. The image near the vehicle, projected on the spherical surface makes it comparatively easy for the driver to figure out a distance between an object and the vehicle. However, since the image far from the vehicle, projected on the cylindrical surface is distorted, the driver has a difficulty in figuring out a distance between an object and the vehicle by using the image.
That is, although a composite image obtained by projecting captured images on a cylindrical surface, a spherical surface or the like is capable of showing an image in a wide field of view, the composite image is quite unlike an image directly viewed by the driver of a vehicle with the eyes. Accordingly such a composite image has a problem of poor visibility because the driver has a difficulty in figuring out a distance between an object and the vehicle by using the image.